The importance of timer circuits in modern small domestic appliances is increasing constantly. In addition, integrating these circuits and realizing them in the form of integrated circuit is of importance for these appliances in order to minimize the dimensions of these appliances and in view of the savings thus obtained.
Such appliances frequently comprise a device which produces generally rectangular pulses spaced by a specific time interval. These pulses are supplied to a counting device. When this device, which has been preset to specific time, has received the number of pulses corresponding to said time, the timer supplies the starting signal for the desired operation.
For such a use it is effective to employ the power frequency as frequency reference, or clock, which frequency in the major countries is maintained very stable at a fixed value: 50 Hz in Europe and 60 Hz in the U.S.A.
Unfortunately, although the basic frequency is maintained stable at a source, the power mains is often disturbed by spurious signals whose frequency is generally higher than a few hundreds of Hz, which spurious signals affect the signal waveform and may disturb the counting process. Spurious signals in the range from 1 to 3 kHz occur very frequently and are very annoying.
For a long time it has been attempted to eliminate said spurious signals by means of low-pass filters, but with the present state of the art it is impossible to integrate such low-pass filters on a monolithic crystal. Indeed, this would require the use of capacitances of several microfarads, which cannot be integrated.
French Patent Application No. 2,363,220 for example describes a filtered power supply for this purpose, which is integrated except for the capacitor.
The present invention provides a solution to the said problems.
It takes into account that filtering is mainly required for logic circuits and that in such circuits sources supplying a small current can readily be realized, in particular in I.sup.2 L technology (integrated injection logic).
It is to be noted that in the present Application "main electrodes" is to be understood to mean those electrodes in which a large current flows, i.e. the emitters and the collectors in bipolar transistors, as distinct from the control electrodes, which in bipolar transistors are constituted by the bases.